The overall goal of this research proposal is to develop a rechargeable subcutaneous transmitter tag for acoustic telemetry of neural recordings in aquatic vertebrates. This device will be used in conjunction with chronically implanted multi-channel sieve electrodes in the toadfish, Opsanus tau. The sieve electrode uses the natural (and accurate) regenerative ability of the teleost VIIIth nerve. Single VIIIth nerve fibers regenerate through gold-lined 5-8 um pores that are electrically coupled to a cable composed of conducting silicon substrate links. These links are ultrasonically bonded to a larger cable terminated by a connector that plugs into a transmitter package mounted on the animal. Recordings have been obtained from several fish via transdermal leads, demonstrating the viability of the sieve as an in situ recording device. The proposed tag is intended to advance sieve-electrode technology one step further and allow monitoring of neural signals from a freely swimming animal in a quasi-natural environment. The specific aims of this research proposal are: 1) to develop a multichannel transmitter tag for subcutaneous implantation on the fish; 2) to develop a receiver system which receives the acoustic signal from the tag at ranges of up to 10 meters and, based on the received acoustic signal, outputs firing time data for the two differential neural recording channels, and determines fish location; and 3) to develop a recharging system that will inductively recharge the tag battery and, by varying the amplitude of the recharging field, allow setting of spike-detection thresholds and selection of electrode channels for recording. The data from the telemetry study is intended to further the understanding of the neural mechanism of equilibrium and hearing.